How to generate a Transparency "Gradient" Shader?(Eevee)
I'm not sure to understand your node organization, in my opinion you should choose between the alpha and the transparent solution, which would give the ColorRamp plugged into the Alpha socket:

or the ColorRamp into the factor of the Mix Shader between the Principled BSDF and the Transparent:

Also, maybe deactivate the material Show Backface option?